1. Field of the Invention
The present invention relates to a stepping motor used as a drive source for a lens drive and the like such as focus and zoom in a digital camera, a camera-fitted mobile telephone, and the like, and an electronic apparatus that includes the stepping motor.
Priority is claimed on Chinese Patent Application No. 200510108180.6, filed Oct. 9, 2005, the content of which is incorporated herein by reference.
2. Description of Related Art
Stepping motors have excellent compatibility with digital control systems, and are recently being frequently used as drive sources for a lens drive and the like such as focus and zoom in electronic apparatuses such as digital cameras and camera-fitted mobile telephones. Use of crow-pole type stepping motors is particularly frequent, since their manufacturing cost can easily be reduced and they are simple to control.
Various types of crow-pole stepping motor have been provided, such as, for example, a two-phase PM type stepping motor that includes two stators (A-phase stator and B-phase stator) incorporated in a cup-shaped housing (e.g., Japanese Unexamined Patent Application, First Publications Nos. 2004-289961 and 2001-78419) and a two-phase PM type stepping motor that does not use a housing (e.g., Japanese Unexamined Patent Application, First Publication No. H03-112356).
As shown in FIGS. 6 and 7, for example, a two-phase PM type stepping motor 30 using a housing includes a rotor 32 consisting of a cylindrical permanent magnet 31 that is multipole magnetized in a circumferential direction R, an A-phase stator 33 and a B-phase stator 34 that are arranged so as to be mutually stacked along an axis L when disposed around the perimeter of the rotor 32, a housing 35 which the A-phase stator 33 and the B-phase stator 34 are accommodated inside of, and a bracket 36 that rotatably supports the rotor 32 after sealing the housing 35 with a lid.
The A-phase stator 33 and the B-phase stator 34 have identical configurations, including an exciting coil 42 formed by winding a coil winding 41 around the outer periphery of a ring-shaped bobbin 40 of resin material, and a pair of yokes 43 that enclose the exciting coil 42 from both sides along the direction of the axis L. A plurality of pole teeth 44 are formed in each of the pair of yokes 43, which enclose the bobbin 40 from both sides while being guided by a guide groove 40a formed in an inner peripheral face of the bobbin 40. At this time, the pole teeth 44 of the pair of yokes 43 are combined with the bobbin with their pitches deviate so that they sequentially arranged in a noncontacting state in the circumferential direction R.
An inner peripheral face of the housing 35 contacts the outer periphery of the pair of yokes 43. Ends of the coil winding 41 wound around the exciting coil 42 are connected to external connectors 40b of the bobbin 40, enabling them to be electrically connected to an external component (not shown), such as a circuit component. Incidentally, the external connectors 40b of the bobbin 40 are exposed to the outside via a notch (not shown) formed in the housing 35.
The conventional crow-pole type stepping motor 30 using the housing 35 in this manner forms the exciting coil 42 by winding the coil winding 41 around the ring-shaped bobbin 40, and can also be electrically connected to the outside by using the bobbin 40.
In contrast, a two-phase PM type stepping motor that does not use a housing includes one yoke unit having an inner yoke and a cup-shaped outer yoke; these yokes are arranged so as to surround the periphery of an exciting coil.
As regards the formation of an exciting coil by winding a coil winding around the outer periphery of a bobbin, this stepping motor is the same as the stepping motor using the housing described above.
However, in the conventional stepping motors described in Japanese Unexamined Patent Application, First Publications Nos. 2004-289961 and 2001-78418 mentioned above, the following problems remain.
Since the exciting coil 42 is formed by winding the coil winding 41 around the bobbin 40 of resin material, the space occupied by the bobbin 40 inside the cross-sectional accommodation space of the exciting coil 42 enclosed by the yokes 43 is magnetically wasteful.
The space occupied by the bobbin 40 is particularly problematic in a small-sized stepping motor whose external diameter is ø6 mm or less, and makes it difficult to secure a large coil volume. This leads to deterioration in the torque characteristic.